Testing, diagnosis, maintenance and calibration of electronic devices often require supplying test signals to, and receiving signals from, components of a Device Under Test (DUT) or Unit Under Test (UUT). When an electronic device is fabricated on one or more circuit boards, electronic components mounted on the circuit boards may not be accessible for testing using existing circuit board mounted connectors. Therefore, connections to components to be tested are made using external electrical probes applied to the exposed leads of the components and/or to a printed circuit board wiring layer.
Automatic testing of electrical circuits requires simultaneous connection to many circuit test points. The automatic testing equipment simultaneously supplies signals to, and receives signals from, combinations of test points. A conventional test fixture used to electrically probe a circuit card of a DUT includes a "bed of nails" having a platform for supporting the circuit card and an array of single headed spring probes. Each spring probe includes a probe head which makes positive electrical contact with an overlying portion of the circuit board being tested. An opposite end of each probe is connected to test equipment through single point wiring.
A conventional single headed electrical test probe is described by Johnston et al., U.S. Pat. No. 5,032,787 issued Jul. 16, 1991, incorporated herein by reference. The Johnston et al. patent describes a test probe assembly including a barrel having a hollow interior and a plunger which slides axially in the barrel. The plunger has an outer portion extending through an open end of the barrel, terminating in a contact tip outside the barrel for contact with a test point and a hollow, elongated receptacle extending through the barrel. The receptacle has a square or rectangular pilot hole so that an elongated fixed guide member in the barrel extends through the pilot hole. The guide member extends through the interior of the barrel away from the pilot hole and has an cuter surface which engages the pilot hole. A spring inside the barrel extends along the guide member and is biased against the internal end of the receptacle inside the barrel.
Axial travel of the Johnston et al. plunger into the barrel is against the spring bias. The outer surface of the guide member engages the correspondingly shaped pilot hole and controls rotational motion of the plunger as it travels along the guide member against the bias of the spring. The guide member is not free to rotate or axially translate through the barrel, i.e., rotate while being depressed in toward the barrel. End 58 of conductive guide member 54 projects out from the end of the barrel to provide an anti-rotational detail for the probe assembly. Cylindrical terminal portion 60 of the end cylindrical section 56 is described as being rigidly affixed to the inside of the barrel. Terminal portion 62 of the guide member projects outside the barrel to provide anti-rotation. Thus, the Johnston et al. probe is useful to connect a dedicated test lead to a single component or conductive layer on one circuit board via rotation of the guide member.
Another example of a conventional spring probe assembly is illustrated in Langgard, U.S. Pat. No. 5,175,493 issued on Dec. 29, 1992. The spring probe assembly includes an outer barrel having an open end and a remote end, an inner core of dielectric material, and an electrical contact spring probe. A shield surrounds the inner core between the barrel and the core and extends the full length of the barrel. The inner core is fixed within the outer barrel, and the shield is biased against the outer barrel. In one embodiment, a double ended probe assembly includes two electrical contact probes. The double ended probe assembly is the same as the single probe assembly, but the axial bore includes two spring probes in back-to-back relationship. An elongated barrel is used which has center connector pins joining the structure together. Thus, Langgard merely utilizes the same structure, and provides no unique structure for creating a double ended probe assembly. In addition, Langgard provides no method or structure whatsoever for effectively and efficiently connecting the shielded contact assembly with a coaxial conductor. Rather, Langgard requires end to end abutment or overlap and soldering techniques to provide a good electrical connection between the probe assembly and a coaxial conductor. Thus, in Langgard, the probe assembly is generally affixed to the coaxial conductor when the coaxial conductor is in use.
Since testing equipment and other electronic equipment must typically be adapted to varied uses, it is often necessary to reconfigure signal connections and condition signals to interface the equipment to a particular DUT. This can be accomplished by dedicated wiring, patch panels, and/or using appropriate signal routing/conditioning interface equipment in the form of a personality board. A personality board is connected between a testing device and a DUT to properly route and condition signals between the two devices. Thus, a testing device is electrically adapted to a particular DUT by using an appropriate personality board. Substitution of personality boards allows a single testing device to be used with a plurality of DUTs.
The testing device is connected to a personality board which, in turn, is connected to a test fixture holding the DUT using conventional electrical connectors and cabling. Thus, the personality board is used to electrically correct two devices. However, the additional wiring used to connect the personality board can impair signal connectivity and degrade the transmitted signals. The added connectors and cables also increase device cost and require additional mounting space on each circuit board and between circuit boards. Further, the device connectors are subject to misalignment and introduce maintenance and reliability problems. Multiple connectors and cabling also complicate the substitution of personality boards. Further, we have discovered that most prior art probes, such as Johnson et al., only provide one-sided connection where, as in Johnson et al. only the guide member rotates.
We have discovered, however, that a need exists for a connector system providing easy installation and replacement of circuit board mounted devices.
We have further discovered that a need exists for a low resistance electrical connector for interfacing circuits and wiring mounted on opposing circuit boards.
In addition, we have discovered that a need exists for a reconfigurable connector system for interfacing various nodes of an electronic device to a corresponding point of a second electronic device without intervening connectors.
We have further discovered that for more critical testing conditions where the transmitted signals are more susceptible to noise or environmental conditions, there is a need to transmit testing signals with higher accuracy.
We have also discovered that for more complicated testing conditions where many signals are required to be transmitted between the DUT and the testing device via the personality board, there is a need to more effectively and efficiently utilize the limited space to transmit these greater number of testing signals.
We have also discovered that it is desirable to effectively and efficiently connect a coaxial shielded contact assembly with a coaxial conductor.
We have also discovered that it is desirable to eliminate the need for end to end abutment or overlap and soldering techniques to provide a good electrical connection between the probe assembly and a coaxial conductor.
We have also discovered that it is desirable to eliminate the need for the probe assembly to be affixed to the coaxial conductor.
We have further discovered that it is desirable that the structure of the coaxial spring probe assembly permit all components to be movably connected to one another.